1. Field of the Invention
The present invention relates to a gas turbine combustor, and more particularly to a multi-nozzle type premixing combustor.
2. Description of the Related Art
Recently, the gas turbine combustor, for example, a steam cooling type combustor capable of realizing low NOx even in a gas turbine of 1500xc2x0 C. class, is attracting wide attention. That is, by cooling the combustor wall by steam, the air hitherto used for cooling of the wall can be used for combustion, and the premixed combustion temperature is suppressed to a level of an air-cooled combustor in spite of temperature elevation in the gas turbine, so that low Nox is realized.
As such a steam cooled combustor, a conventional example of a multi-nozzle type premixing combustor as shown in FIG. 5 is known. In this combustor a nozzle outer tube 7 for forming and injecting a premixed gas of main fuel from a main fuel nozzle 5 and combustion air from a main swirler 6 is divided and disposed in plural sections around a cone 4. The cone 4 forms a diffusion flame by reaction between pilot fuel from a pilot fuel nozzle 2 and combustion air from a pilot swirler 3 and being disposed in the center of the section of a combustor inner tube 1.
In the main fuel nozzle 5, as shown in FIG. 4, the fuel is injected from plural nozzle holes 5a (about 1.0 mm in diameter) opened in the nozzle main body wall, and is mixed with the air flowing in the nozzle outer tube through the main swirler 6, thereby forming a premixed gas.
In FIG. 4 and FIG. 5, the arrows show the flow of fuel and air.
However, in such conventional multi-nozzle type premixing combustor, as shown in FIG. 3, since the nozzles holes 5a of the main fuel nozzle 5 are formed in three positions on the outer periphery of the combustor inner tube 1 and in two positions at the inner side, the fuel distribution to the outer periphery increases. The fuel may bounce on an elliptical extended pipe 7a (which is provided for preventing back-fire by raising the gas flow velocity) due to circumferential swirling flow caused by a swirler, and collide against the wall of the combustor inner tube 1 (see arrow in FIG. 3).
As a result, liquid fuel drops may deposit on the wall of the combustor inner tube 1 (see hatching (xe2x96xa1) in FIG. 3), and the internal pressure may fluctuate, spoiling combustion stability, or the metal temperature may be raised by self-ignition, thereby breaking the wall of the combustor inner tube 1 (see broken part (T) in FIG. 3).
The invention is devised in the light of such background, and it is hence an object thereof to present a gas turbine combustor capable of improving fuel distribution from a main fuel nozzle, suppressing internal pressure fluctuation and elevation of inner tube metal temperature, and realizing combustion stability and improvement of the durability of the combustor.
To achieve the object, the gas turbine combustor of the invention is a multi-nozzle type premixing combustor as follows. A nozzle outer tube for forming and injecting a premixed gas of main fuel and combustion air is disposed in plural sections around a cone for forming a diffusion flame by reaction between pilot fuel and combustion air. The cone is disposed in a center of a section of a combustor inner tube. Nozzle holes of a main fuel nozzle for injecting the main fuel are opened and formed more at the inner side than at the outer periphery of the combustor inner tube in the nozzle main body wall, and the fuel distribution to the outer periphery is decreased.